1. Field of the Invention
This invention relates to an electrolytic processing device and a substrate processing apparatus provided with the electrolytic processing device, and more particularly to an electrolytic processing device useful for processing a conductive material present on a surface of a substrate, especially a semiconductor wafer, or for removing impurities adhering to a surface of a substrate, and a substrate processing apparatus provided with the electrolytic processing device.
2. Description of the Related Art
In recent years, instead of using aluminum or aluminum alloys as a material for forming interconnection circuits on a substrate such as a semiconductor wafer, there is an eminent movement towards using copper (Cu) which has a low electric resistance and high electromigration resistance. Copper interconnects are generally formed by filling copper into fine recesses formed in a surface of a substrate. There are known various techniques for forming such copper interconnects, including CVD, sputtering, and plating. According to any such technique, a copper film is formed on substantially an entire surface of a substrate, followed by removal of unnecessary copper by performing chemical mechanical polishing (CMP).
FIGS. 85A through 85C illustrate, in sequence of process steps, an example of forming such a substrate W having copper interconnects. As shown in FIG. 85A, an insulating film 2, such as a silicon oxide film/a film of silicon oxide (SiO2) or a film of low-k material, is deposited on a conductive layer 1a in which electronic devices are formed, which is formed on a semiconductor base 1. A contact hole 3 and a trench 4 for interconnects are formed in the insulating film 2 by performing a lithography and etching technique. Thereafter, a barrier layer 5 of TaN or the like is formed on an entire surface, and a seed layer 7 as an electric supply layer for electroplating is formed on the barrier layer 5.
Then, as shown in FIG. 85B, copper plating is performed onto a surface of the substrate W to fill the contact hole 3 and the trench 4 with copper and, at the same time, deposit a copper film 6 on the insulating film 2. Thereafter, the copper film 6 on the insulating film 2 is removed by performing chemical mechanical polishing (CMP) so as to make a surface of the copper film 6 filled in the contact hole 3 and the trench 4 for interconnects and a surface of the insulating film 2 lie substantially in the same plane. An interconnection composed of the copper film 6 as shown in FIG. 85C is thus formed.
Components in various types of equipment have recently become finer and have required higher accuracy. As sub-micro manufacturing technology has commonly been used, properties of materials are largely influenced by a processing method. Under these circumstances, in such a conventional machining method that a desired portion in a workpiece is physically destroyed and removed from a surface thereof by a tool, a large number of defects may be produced to deteriorate properties of the workpiece. Therefore, it becomes important to perform processing without deteriorating properties of materials.
Some processing methods, such as chemical polishing, electrolytic processing, and electrolytic polishing, have been developed in order to solve this problem. In contrast with conventional physical processing, these methods perform removal processing or the like through chemical dissolution reaction. Therefore, these methods do not suffer from defects, such as formation of an altered layer and dislocation, due to plastic deformation, so that processing can be performed without deteriorating properties of materials.
Chemical mechanical polishing (CMP), for example, generally necessitates a complicated operation and control, and needs a considerably long processing time. In addition, a sufficient cleaning of a substrate must be conducted after a polishing treatment. This also imposes a considerable load on slurry or cleaning liquid waste disposal. Accordingly, there is a strong demand for omitting CMP entirely or reducing a load upon CMP. Also in this connection, it is to be pointed out that though a low-k material, which has a low dielectric constant, is expected to be predominantly used in the future as a material for an insulating film of a semiconductor substrate, the low-k material has a low mechanical strength and therefore has difficulty in enduring stress applied during CMP processing. Thus, also from this standpoint, there is a demand for a technique that enables flattening of a substrate without applying any stress thereto.
Further, a method has been reported which performs CMP processing simultaneously with plating, viz. chemical mechanical electrolytic polishing. According to this method, mechanical processing is performed to a growing surface of a plating film, causing a problem of denaturing of a resulting film.
In a case of the above-mentioned electrolytic processing or electrolytic polishing, processing proceeds through an electrochemical interaction between a workpiece and an electrolytic solution (aqueous solution of NaCl, NaNO3, HF, HCl, HNO3, NaOH, and the like). Since an electrolytic solution containing such an electrolyte must be used, contamination of a workpiece with the electrolyte cannot be avoided.
In recent years, metals of the platinum group or their oxides have become candidates for an electrode material for use in forming a capacitor, which utilizes a high dielectric or ferroelectric material, on a semiconductor substrate. Among them ruthenium, because of its good film-forming properties and good processibility for patterning, is being progressively studied as a feasible material.
A ruthenium film can be formed on a substrate generally by performing sputtering or CVD. In either method, deposition of the ruthenium film on an entire front surface of a substrate, including a peripheral region, is performed. As a result, a ruthenium film is formed also in the peripheral region of the substrate and, in addition, a back surface of the substrate is unavoidably contaminated with ruthenium.
The ruthenium film formed on or adhering to the peripheral region or back surface of the substrate, i.e. a non-circuit region of the substrate, is not only unnecessary, but can also cause cross-contamination during later transfer, storage and various processing steps of the substrate whereby, for instance, performance of a dielectric material can be lowered. Accordingly, during a process for forming a ruthenium film or after peforming some treatments of a formed ruthenium film, it is necessary to completely remove unnecessary portions of this ruthenium film. Further, in a case of using ruthenium as an electrode material for forming a capacitor, a step for removing part of a ruthenium film formed on a circuit region of a substrate is needed.